JP-B-4309439 and JP-B-4565023, for example, have proposed a system for picking up an object using a robot, which initially images, using an imaging device, a state where a plurality of objects (for example, components) is randomly piled up. Subsequently, the system detects one of the plurality of objects based on an image imaged by the imaging device. Then, the system picks up the detected object using a robot. In such a system, an object makes various faces (front surface, rear surface, or side surface) thereof face an imaging surface of an imaging device (hereinafter, referred to as an “imaging surface”). The brightness of an object contained in an image imaged by the imaging device (hereinafter, referred to as the “brightness of an object”) in the case where a face of the object is parallel to the imaging surface is larger than in the case where the face of the object is not parallel to the imaging surface (for example, a case where the face of the object is inclined to the imaging surface). Since various faces of the object face the imaging surface, the brightness of the object varies. As a result, it is difficult to detect the object in some cases.
For example, when the face of the object is parallel to the imaging surface, most of light having entered the object from an illuminating device or the like is reflected in a direction toward the imaging surface. As a result, most of light having been reflected from the object enters the imaging surface. Therefore, the brightness of the object increases and then halation occurs in an image, resulting in a possibility of difficulty in detection of the object. On the other hand, when the face of the object is not parallel to the imaging surface (for example, when the face of the object is inclined to the imaging surface), most of light having entered the face of the object from the illuminating device or the like is reflected to a direction other than the imaging surface. As a result, most of light having been reflected from the object does not enter the imaging surface. Therefore, the brightness of the object decreases, resulting in a possibility of difficulty in detection of the object. In this manner, the brightness of the object varies with a ratio where light reflected from the object enters the imaging surface.
On the other hand, there have been proposed devices for avoiding a situation where the brightness of an object excessively increases due to the fact that the face of the object is parallel to the imaging surface and a situation where the brightness of the object excessively decreases due to the fact that the face of the object is inclined to the imaging surface. JP-A-4-32381, for example, has proposed an imaging device for acquiring an image having large dynamic range, for example, via exposure performed for a plurality of exposure times, and JP-A-2010-134915, for example, has proposed an image processing device for generating an image having large dynamic range from a plurality of images acquired via imaging performed for a plurality of exposure times.
However, the conventional imaging device and image processing device have a problem that a difference in the brightness of an object, in other words, the contrast of an image decreases, resulting in difficulty in detecting the object.
An object of the present invention is to provide an image processing device and an image processing method in which the brightness of an object does not vary according to an orientation of the object without a decrease in the contrast of an image imaged by an imaging device.